1. Field of the Invention
The present invention relates to an acceleration sensor and, more particularly, to a semiconductor acceleration sensor with improved shock resistance.
2. Description of the Related Art
In order to implement various types of control in moving bodies such as automobiles and ships and in robots, mechanical fabrication devices, or mobile devices that are grasped and used by a user, such as notebook PCs, portable telephones, PDA (Personal Digital Assistant), DVC (Digital Video Camera), DSC (Digital Still Camera), for example, it is essential to detect the stress acting on all or part of the target body in correspondence with the objective of the control. By sensing the stress on the basis of the acceleration acting on all or part of the target, it is possible to sense the acceleration.
A variety of devices for detecting this stress or acceleration have been conventionally developed, of which one device is known in which a gauge resistor is formed on the semiconductor substrate as a detection element and which converts the mechanical strain produced on the basis of a force acting on the that is supplied from outside into an electrical signal as a result of the piezoresistive effect (“Development of three-weight sensor” ‘Invention’ Journal pages 52 to 63, published by the Invention Society on September 2003).
In addition, the fact that it is also possible to use a change in the electrostatic capacity corresponding with strain instead of using the piezoresistive effect of the gauge resistor is explained in “Development of three-weight sensor” ‘Invention’ Journal pages 52 to 63, published by the Invention Society on September 2003.
In particular, the characteristic of the invention that is described in “Development of three-weight sensor” ‘Invention’ Journal pages 52 to 63, published by the Invention Society on September 2003 is the fact that it is possible, by means of force sensors for a plurality of axial directions formed on a semiconductor substrate, to constitute sensors of a plurality of types, that is, sensors of four types, namely, a three-axis force sensor, a three-axis acceleration sensor, a three-axis angular speed sensor, and a six-axis motion sensor by means of one device.
Proposals have been made for each of a variety of problems relating to a semiconductor acceleration sensor that employs the principles mentioned in “Development of three-weight sensor” ‘Invention’ Journal pages 52 to 63, published by the Invention Society on September 2003. One of these various problems is that a large unforeseen shock can sometimes be applied as a result of the environment in which the acceleration sensor is applied (depending on what kind of device the acceleration sensor is used in). In such a case, there is a risk that the weight will be displaced greatly and the gauge resistor will be accordingly damaged.
In order to eliminate this inconvenience, a constitution in which a stopper that limits the displacement of the weight is provided has been proposed (Japanese Patent Application Laid Open No. 2000-304762).
Here, as indicated in “Development of three-weight sensor” ‘Invention’ Journal pages 52 to 63, published by the Invention Society on September 2003 and in Japanese Patent publication H8-7228, an acceleration sensor with a structure in which the relationship between the weight and support portion is reversed, that is, in which the support portion is placed in the center of the acceleration sensor and the weight is suspended by means of a beam portion at the periphery of the support portion, is known. In the following description, an acceleration sensor with this structure is expediently referred to as a parasol-type acceleration sensor.
An acceleration sensor with a parasol-type acceleration sensor structure in which this support portion is placed in the center is illustrated in “Development of three-weight sensor” ‘Invention’ Journal pages 52 to 63, published by the Invention Society on September 2003, Japanese Patent Application Laid Open No. 2000-304762, and Japanese Patent publication H8-7228. However, the application of a structure that limits shocks of the acceleration sensor shown in Japanese Patent Application Laid Open No. 2000-304762 to a parasol-type acceleration sensor is not suggested.